-LRB- CNN -RRB- -- Nearly a million acres were burning as 21 wildfires raged in the Pacific Northwest on Sunday , fire officials said .

The unconfined fires in Oregon and Washington , mostly ignited by lightning from thunderstorms that swept through the region a week ago , covered 942,247 by Sunday , Northwest Interagency Coordination Center spokeswoman Carol Connolly said .

The 21 large fires are the most the region has seen on the landscape at one time , she said .

According to Okanogan County , Washington , Sheriff Frank Rogers , one person died attempting to protect his home from the flames .

Authorities arrested two people over the weekend on suspicion of arson , the sheriff said . They set backfires to protect their property .

More than 150 structures have been lost . The sheriff expects that number to go up .

`` I 've been here 30 years , never seen anything like this , '' Rogers said .

According to Connolly , firefighters from across the United States , including Mississippi , Illinois , New Mexico , Utah and Montana , have joined the battle , bringing to 8,928 the number of people involved in trying to contain the fires . There are 35 `` hot shot '' crews involved , she said .

Health officials in Washington and Idaho are warning residents that smoke drifting eastward from the Washington wildfires would create unhealthy air .

`` The biggest health threat comes from the fine particles in smoke , '' the National Weather Service said . `` These can cause burning eyes , runny nose , bronchitis and other illnesses . Smokey air can also aggravate heart and lung disease , and even lead to death . ''

Hundreds evacuated as Washington wildfire grows

What to know about wildfires

CNN 's Dave Alsup and Janet DiGiacomo contributed to this report .

@highlight

Wildfires cover 942,247 acres in the Pacific Northwest on Sunday

@highlight

The 21 large fires are the most the region has seen at one time , an official says

@highlight

Health officials in Washington and Idaho warning smoke creates unhealthy air